Big birds The tallest and heaviest ever known penguin stood nearly a metre and half tall and tipped the scales at around 60 kilograms, according to a 27-million-year-old fossil found in New Zealand.

The penguin, Kairuku grebneffi lived in what is now New Zealand and likely speared fish and squid with its curved beak. In comparison, today's largest penguin is the Emperor penguin, which measures one metre tall and weighs approximately 40 kilograms.

Yet another new big fossil penguin, Kairuku waitaki, was also recently discovered. It lived alongside K. grebneffi. The finds by an international team of researchers was described in the latest Journal of Vertebrate Paleontology.

"The Kairuku penguins were the last generation of so-called 'giant penguins', the term indicating any fossil penguins that were much larger than the living largest Emperor penguin," says co-author Tatsuro Ando of the Ashoro Museum of Paleontology in Japan.

Ando says that these big flightless birds emerged around 50 million years ago and thrived for about 25 million years before dying out. It remains a mystery as to why they disappeared, "but probably the drastic change in palaeoenvironment was the cause of their demise," he says.

The researchers, led by Daniel Ksepka of North Carolina State University, analysed the near-complete fossils for the penguins, which were unearthed at New Zealand's Waitaki Region. This area was known as Zealandia during prehistoric times, and it was a veritable penguin paradise.

"For much of its history, New Zealand has been sitting in the middle of the Southern Ocean, the sea that circles Antarctica," says co-author Ewan Fordyce of Otago University. "For millions of years, it has provided suitable land for rookeries (breeding grounds) and access to rich food resources in nearby seas."

Appeared after the dinosaurs

To this day, New Zealand is a centre of diversity for penguins. Out of the 17 existing species of penguin, six live and breed in New Zealand.

The two new fossil species, from a distance, would have looked like modern penguins, says Fordyce.

"Up close, however, it is clear that both species had relatively longer bills and a more slender body than in living species," he says. "The wing was probably able to flex a little more."

Their long beaks would have enabled these penguins to spear prey, such as fish and squid. Sharks and shark-toothed dolphins, a type of prehistoric super strong dolphin with heavily toothed jaws, probably hunted the enormous penguins, which could have snapped back with their beaks.

The research team, which also included Craig Jones, mentioned that the oldest known penguin so far is Waimanu from New Zealand.

"It lived [between] 55 to more than 60 million years ago, not long after the extinction of dinosaurs," says Fordyce.

Ksepka says one theory holds that penguins lost their ability to fly after the Cretaceous mass extinction.

DNA evidence indicates that the closest living relatives of penguins are tubenose seabirds, such as albatrosses and petrels. Since the latter can dive to significant depths, the scientists suspect that the first penguins could both fly and dive underwater.

Nicholas Pyenson, curator of Fossil Marine Mammals at the Smithsonian's National Museum of Natural History, told Discovery News that the authors of the new paper "are spot on with their conclusions about the early evolution of penguins."

Stig Walsh, senior curator of Vertebrate Paleontology at National Museums Scotland, suspects that even taller penguins might be unearthed in the future but, for now, K. grebneffi is the height and weight champ.